I made a batch of halfplate cardboard pinhole cameras for my childrens' school 25 years ago. My (dress-rehearsal) attempts at reversal processing were not successful, so we made single-weight paper negatives, then contact prints. I found that the low contrast and fuzzyness arose from the piercing of the aluminium foil we used to fabricate the pinhole because the needle formed a tunnel with a reflective bore. We found it better to pierce a small X with a scalpel and, through a magnifier, fold four foil flaps away from the hole. Etching copper shim would probably work better. We found that a 0.8mm hole (an 'aperture' of about f/128 or f/180) gives the best compromise between sharpness and exposure time. Using this aperture with medium format might show excessive diffraction.
The long exposures showed only the vehicles that parked on the double yellow lines. But we couldn't read the number plate!
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